provided the denominator is nonzero. In particular, for \(\tau \rightarrow \pm \infty \) , this stepsize converges to the BB1 stepsize, which is expressed as (cf., e.g., [1]})
\( \alpha _{k}^{\rm {BB1}} = \frac{\sum _i \, (\gamma _{i}^{k-1})^2\ \lambda _i}{\sum _i \, (\gamma _{i}^{k-1})^2}.\) 
